Sen. Pat Toomey (R-Pa.) endorsed former Rep. Mark Neumann (R-Wis.) today in his campaign for Wisconsin's open Senate seat. Toomey is the fifth GOP Senator from the party's more conservative wing to endorse Neumann.

"Congressman Mark Neumann is a man of courage and principle, and I am proud to endorse him in his run for the U.S. Senate," Toomey said in a press release. “In this era of skyrocketing deficits and stagnant economic growth, Mark is exactly the kind of leader we need in Washington."

Neumann, who is locked in a tight primary race against three GOP competitors, is thought to have the most conservative record of the Republican candidates. He has been endorsed by conservative activists groups such as the Club for Growth and the Senate Conservatives Fund in addition to getting the backing of Republican Sens. Jim DeMint (S.C.), Mike Lee (Utah) and Rand Paul (Ky.).

Despite the high profile endorsements, Neumann trails former Gov. Tommy Thompson by a substantial margin in recent polls. The winner of the Aug. 14 GOP primary will face presumptive Democratic nominee Rep. Tammy Baldwin (Wis.) in the November general election.

Conservatives, meantime, took aim at Thompson over the health care law.

A newly released video promoted online by the Club for Growth shows Thompson saying in a 2006 interview that he supports the individual mandate implemented in Massachusetts.

"The truth of the matter is it's just like automobile insurance," Thomspon says in the C-SPAN video. "You gotta have coverage. And if you're going to be able to cover the uninsured you're going to have to have some degree of a mandate to cover the uninsured."

http://youtu.be/gNh2vVrlLdw

Darrin Schmitz, a Thompson campaign spokesperson, pointed to Thompson's 2008 testimony before the Senate Finance Committee to push back on the video.

"We have seen in Massachusetts that the individual mandate approach is not effective at covering the most vulnerable part of the population, that part of the population which needs coverage the most," Thompson said in 2008.

Thompson also renewed his vow to work to repeal the Affordable Care Act following the Supreme Court's decision.

"My first vote as a U.S. Senator will be for the full repeal of Obamacare," he said in a statement. "I will use every measure available to block any vote in the next term of the Senate until a full Obamacare repeal vote is taken."

Neumann and businessman Eric Hovde also released statements vowing to repeal the law. Thompson, Neumann, Hovde and Wisconsin Assembly Speaker Jeff Fitzgerald are locked in a competitive GOP primary.